This invention relates to current interrupters for use in electrical power distribution systems and particularly to full range electrical fuses.
Full range electrical fuses provide a relatively inexpensive means of current interruption in a large variety of applications. Such fuses may be triggered by currents which exceed the rated current of the fuse or they may be triggered externally in which case they can interrupt currents below their rated currents. For example, in chemically activated full range fuses, a trigger circuit is used to fire a chemical charge which cuts the fuse element and interrupts the current in the circuit protected by the fuse.
One problem associated with the full range fuses are their susceptibility to triggering upon the occurrence of lightning or switching generated current surges. Typically, the trigger circuit which fires the chemical charge is isolated from the main fuse element by an air gap in order to prevent any current from flowing in the trigger circuit unless the main fuse element opens due to fault current or overload. Under lightning, switching or other surge current producing conditions, due to the high rate of rise of current produced under such conditions, higher voltage will be induced across the fuse inductance. This voltage could cause the air gap to spark-over and effect operation of the fuse. Although full range fuses can interrupt currents below their rated current, operation of fuses during lightning storms or as a result of switching generated current surges should be minimized in order to reduce power shutdown to consumers.